Study On The Seismic Response Of Large-scale Submerged Tunnel And Auxiliary Shaft

ABSTRACT:With the rapid development of the underwater transportation, the destruction problem of the tunnel and shaft built in the seismic activity region will be faced, and the aseismic safety problem needs to be solved especially for the large-scale structure in deep water and loose soil. However, the seismic response analysis of water-soil-structure system is a complicate multi-field coupling issue, and now it’s still at the inicial stage. Based on the wave propagation theory, soil dynamics theory and the theory of structural dynamics, the mechanism model of structure is established under the seismic loading, the seismic response of structure is investigated combining with the numerical simulation analysis method. The main work and conclusions are as follows:(1) Starting from the hydrodynamic pressure of underwater cylindrical structure, the corresponding calculation formulas are provided considering the effects of the surface wave and compressibility of water. Through the example analyses we conclude that:for the large underground structures, neglecting the influence of surface wave and water compressibility on the seismic response of the tunnel is feasible.(2) Based on the elastic foundation beam theory, with additional mass simulation of dynamic water pressure, the simplified analysis model is given considering the self-weight of the structure and seismic loading, and the structure internal force calculation formulas are derived in consideration of the tunnel and the shaft connection joint, and the use of the transfer matrix method to solve. Then the effects of wall thickness, water depth and other factors are analyzed on the dynamic response of tunnel shaft using the simplified model, through the factor analyses we get that:reducing the wall thickness of shaft, increasing the shaft buried depth is beneficial to reducing the internal force of the structure, while the increase of water depth with the opposite effect.(3) Considering the viscoelastic artificial boundary condition, the finite element model of water-soil-structure system is put forward, the calculation program is compiled, and the seismic response mechanism of tunnel and shaft in sand and silt foundation is analyzed considering the direction of seismic excitation and the main related factors. Furthermore, the effect of joint stiffness on the structural internal force and deformation is discussed.(4) Through the study of stability measures of tunnel and auxiliary shaft in loose soil foundation, we conclude that:the style of gravity foundation is beneficial to the structural stability, but increases the base stress simultaneously. So for the stability design of large underground structure, two aspects of enhancing the bearing capacity of foundation and seismic stability of structure should be considered.